This invention relates to antifouling coating compositions. This invention further relates to improved coating compositions for combatting the attachment and growth of barnacles, algae, and other undesirable organisms on surfaces exposed to a marine environment, particularly the submerged sections of ships and pleasure craft.
Triorganotin compounds of the formula R.sub.3 SnX or (R.sub.3 Sn).sub.2 Y are known to be effective toxicants for antifouling coatings. Preferably R represents an alkyl radical containing between 1 and 4 carbon atoms or a phenyl radical. X and Y can represent a variety of suitable monovalent or divalent anionic radicals, respectively, including halogen (fluorine, bromine or chlorine), oxygen, sulfur and residues of carboxylic- or mercaptocarboxylic acids. When R represents a linear alkyl radical containing more than 4 carbon atoms or a cycloalkyl radical the compound is often not sufficiently toxic or is not leached out from the coating by sea water in large enough quantities and/or at a fast enough rate to provide control of barnacles and algae. These organisms attach themselves to the submerged portion of a vessel's hull and propagate to the extent that they interfere with the ability of the vessel to attain maximum speed and maneuverability. The vessel must be taken out of the water periodically and the accumulated organisms removed by scraping or sand blasting, following which the hull is repainted. This is a time-consuming and costly procedure.
An objective of this invention is to provide coating compositions which more effectively utilize certain organotin toxicants.
It has now been found that the performance of antifouling coating compositions containing as the toxicant certain asymmetric triorganotin compounds wherein 1 or 2 of the 3 hydrocarbon radicals bonded to the tin atom is generally associated with relatively inactive organotin toxicants is significantly improved when the asymmetric triorganotin compound is used in combination with a mixture of a suitable film-forming polymer and rosin in specified proportions as the film-forming component. The relative concentration of rosin in this mixture is inversely proportional to the solubility of the triorganotin compound in sea water, which can be readily determined using known techniques.